Axial self-diffusivities of water molecules (at loadings ranging from near-infinite dilution to near-saturation) were calculated using molecular dynamics simulations, whereas adsorption properties were computed using grand canonical Monte Carlo simulations and were also compared to experimental data. The transport diffusivities were evaluated using the Darken approximation. Water transport in these nanotubes at room temperature was observed to occur via Fickian diffusion. The self-diffusivity decreased with increasing water content, whereas the transport diffusivity exhibited a maximum at intermediate water contents. The diffusivities were comparable to the diffusivity of bulk liquid water and were thus considerably higher than in other nanoporous aluminosilicates such as zeolites. The computed adsorption isotherms exhibited inflections at low partial pressures (∼6mm Hg) with a large fraction of adsorption occurring in the pores of nanotubes displaying marked hydrophilicity. As a combined result of the relatively fast Fickian diffusion of water, hydrophilicity of the nanotubes, and the short nanotube lengths, the diffusive water flux through an aluminosilicate nanotube film was predicted to be 102 to 103mol/m2s; even for very low pressure differentials across the membrane.

Water in Single-Walled Aluminosilicate Nanotubes: Diffusion and Adsorption Properties. S.Konduiri, H.M.Tong, S.Chempath, S.Nair: Journal of Physical Chemistry C, 2008, 112[39], 15367-74